Filter device with filter element

ABSTRACT

The invention relates to a filter device for filtering fluid particularly in the form of an aqueous urea solution, comprising a filter housing ( 1 ) and a filter element ( 11 ) arranged therein, as well as a compensating element ( 31 ) for compensating fluctuations in the pressure and/or volume of the fluid, and characterised in that at least one elastically-flexible membrane ( 31 ) serves as the compensating element, the membrane wall of which is held in a retaining part ( 35 ) and maintains a separation between the fluid and a compressible filling medium such as a working gas. 
     Eine Filtervorrichtung zum Filtern von Fluid, insbesondere in Form einer wässrigen Harnstofflösung, mit einem Filtergehäuse ( 1 ) und einem darin angeordneten Filterelement ( 11 ) sowie einem Ausgleichselement ( 31 ) zum Kompensieren von Druck- und/oder Volumenschwankungen des Fluids, ist dadurch gekennzeichnet, dass als Ausgleichselement mindestens eine elastisch nachgiebige Membran ( 31 ) eingesetzt ist, deren Membranwand in einem Halteteil ( 35 ) gehalten eine Trennung zwischen dem Fluid und einem kompressiblen Befüllmedium, wic einem Arbeitsgas, vornimmt.

The invention relates to a filter device for filtering fluid, particularly in the form of an aqueous urea solution, comprising a filter housing and a filter element arranged therein, as well as a compensating element for compensating fluctuations in the pressure and/or volume of the fluid. The invention further relates to a filter element which, in particular designed as an interchangeable element, can preferably be used for such a filter device.

DE 10 2012 020 431 A1 discloses a filter device comprising at least one filter element, through which a fluid to be purified can flow with a determinable fluid operating pressure and which can be accommodated in a housing, wherein the fluid pressure prevailing at the respective filter element may exhibit general pressure increases or pressure peaks which are damaging to the respective filter element, in particular to the filter material thereof, and which can be reduced and/or smoothened by means of a compensation device which acts directly upon the respective filter element and which has at least one flexible compensation element that enables the volume of the fluid chamber of the housing to be increased in accordance with a pressure peak or pressure increase. In the prior art solution, the flexible compensating element is arranged upstream between the outside of the filter material of the filter element and the adjacent inner wall of the housing, i.e. the fluid passage between the compensating element and the filter element is connected to the fluid inlet and the fluid supply is thus arranged upstream, whereas the fluid filtered by the filter element is discharged from the filter device downstream via a centrally arranged opening in the end cap.

In the prior art solution, the flexible compensating element is configured in the nature of a bowl inserted in the housing of the filter device and is preferably made of a cellular rubber material. The prior art solution can also be used to compensate for the increase in volume of a freezing aqueous urea solution (as used in so-called SCR exhaust systems, particularly in automotive engineering) via the cellular rubber compensating element in order to help prevent damaging pressure influences exerted on the sensitive filter element material by the increase in volume, which could otherwise lead to the inoperability of the filter device, in particular if the freezing of the fluid material results in a tear or the like in the filter element material. Because of the relatively rigid material properties of the cellular rubber used for the compensating element, the compensating mechanism of the prior art filter device, acting as a pulsation damper, is suitable for smoothing out or attenuating sudden pressure spikes, but is hardly suitable for compensating the increase in volume that occurs in the filtering of aqueous urea solutions in the event of freezing.

Proceeding from these difficulties, the present invention addresses the problem of providing a filter device of the aforementioned type in which the compensating element provides particularly effective and reliable freeze protection during operation using freezable fluids such as an aqueous urea solution.

According to the invention, this object is achieved by a filter device that has the features of claim 1 in its entirety.

According to the characterizing part of claim 1, an essential feature of the invention lies in the fact that as a compensating element, use is made of at least one elastically flexible diaphragm, the diaphragm wall of which is held in a retaining part, maintaining a separation between the fluid and a compressible filling medium such as a process gas. In a particularly advantageous manner a compensating mechanism in the form of a diaphragm accumulator is achieved in that way, which when the filling pressure of the filling medium (such as the process gas) is adjusted to the pressure of the operating fluid, enables the necessary increase in volume in the event of freezing, but without a more powerful pressure surge that would damage the filter element.

Because the compensating element in the prior art solution, as explained, is arranged upstream inside the housing of the filter device, i.e., on the unfiltrate side, it takes up a relatively large amount of construction space in the filter housing. In an advantageous fashion, the arrangement in the filter device according to the invention can be made in such a way that the diaphragm is arranged on the downstream filtrate side of the filter element. By virtue of the entire compensating mechanism (i.e., the diaphragm plus the compressible filling medium, such as process gas) being shifted into the housing interior surrounded by the filter medium, the compensating mechanism does not contribute to enlarging the outer periphery of the filter housing surrounding the outside of the filter medium.

With particular advantage, the diaphragm can be configured cup-like, spherical shell-like, or dome-like and consist of ethylene propylene diene monomer rubber (EPDM) or hydrogenated acrylonitrile butadiene rubber (HNBR). These materials are especially well-suited for filter devices for aggressive fluids such as aqueous urea solutions. Nitrile butadiene rubber or other elastomers can obviously be used for other applications. A bulge, which engages in an assignable recess on the retaining part in a form-fitting manner, can be provided on the edge of the diaphragm for a particularly secure anchoring thereof.

With particular advantage, provision can be made of a cup-shaped diaphragm, which is of similar design as a diaphragm used in diaphragm-type hydraulic accumulators. The possibility of using an identical component that is already available as a ready-made product for producing accumulators as a diaphragm permits the filter device according to the invention to be produced in a particularly cost-effective manner.

Exemplary embodiments, in which an at least partially fluid-permeable supporting body is arranged on the outer contour of the given diaphragm and essentially follows the outer contour thereof, are characterized by particularly high operational reliability over a long operating lifespan.

In particularly advantageous exemplary embodiments, the compensating element has two identically configured diaphragms that are fastened on opposite sides of the retaining part, which is configured as a hollow part and receives a process gas, preferably in the form of nitrogen gas, as a filling medium. The retaining part can advantageously have a filling mechanism for the compressible filling medium.

The compensating element can be surrounded at a predefinable radial distance by a cylindrical support tube having fluid passages, the outer periphery of which supports the filter element. This support tube can form a component of the individual filter element.

This filter element can have two end caps between which the preferably pleated, multi-layer filter medium extends, of which at least one end cap at least partially fills in the filter housing, preferably at the bottom, in order to prevent dead volume and/or the other end cap is penetrated by a preferably temperature-controllable receiving block for securing the retaining part inside the filter housing. With particular advantage, such exemplary embodiments are suited for use in SCR exhaust systems because controlling the temperature of the receiving block while the filter device is operating under freezing conditions ensures that the aqueous urea solution remains in the liquid state by virtue of the retaining block being heated. In this way, the reliable operation of the SCR exhaust system is ensured, while the filter element is simultaneously protected from damage by the interchangeable element during downtimes under freezing conditions and in the event that the urea solution freezes.

The subject matter of the invention is also a filter element, in particular one designed as an interchangeable element, that is preferably provided for a filter device according to any one of claims 1-10 and that has the features of claim 11.

Below the invention is explained in detail with reference to an exemplary embodiment depicted in the drawing. The single figure of the drawing shows a longitudinal section of the exemplary embodiment, which is depicted with the filter head removed from the bowl-like filter housing.

The invention is described using the example of a filter device that can be used particularly advantageously in SCR exhaust systems for filtering aqueous urea solutions. The exemplary embodiment has a filter housing 1 in the form of a circular cylindrical bowl having a closed, dished head 3 and an open upper end 5. A housing lid or head that can be screwed onto the housing 1 on the upper end 5, which has been omitted in the figure, has a fluid inlet and a fluid outlet for introducing the fluid to be filtered into the housing 1 via an inlet area, which is designated by a flow arrow 7 in the figure, and for discharging it from the housing 1 via an outlet area 9, which is designated by a flow arrow 9.

A filter element 11 is removably accommodated therein, which has a filter medium 13 forming a hollow cylinder that is preferably pleated and constructed of multiple layers in the manner typical of such filter devices and extends between an end cap 15 (at the top in the figure) and a lower end cap 17. The filter element 11 is accommodated in the housing 1 in such a way that the outside of the filter medium 13 is situated at a distance from the housing wall so as to form a space 19 surrounding the filter medium 13, which adjoins the fluid inlet area designated by the flow arrow 7 and forms the dirty side or the unfiltrate side in the filtering process. The lower end cap 17 has a closed, relatively large-volume shape, the outside of which rests on the inner surface of the dished head 3 of the housing 1, if the filter element 11 is installed. The upper end cap 15 has the shape of an annular body surrounding a central opening 21, having a connecting piece 23 projecting axially upward along the opening 21, on the outside of which an O-ring 25 is situated, which forms the seal between the inflow area (flow arrow 7) and the outflow area (flow arrow 9) for a closed housing 1.

A support tube 27 having fluid outlets is located on the inside of the filter medium 13, the ends of which support tube, along with the ends of the filter medium 13, are accommodated in the end caps 15 and 17 forming a setting, wherein the ends of the filter medium 13 and of the support tube 27 are secured in the end caps 15 and 17 by gluing, for example. A compensating mechanism, which has two diaphragms 31 as a compensating element, is arranged in the interior filter cavity 29 adjoining the inner surface of the support tube 27 that forms the downstream filtrate side. The volume of the interior filter cavity 29 is delimited at the lower surface facing the bottom 3 by the end cap 17, and at the upper end 5 of the filter housing 1 by a holding part 33, which also forms the mount for the compensating mechanism situated in the filter cavity 29. In order to keep the dead volume of the filter cavity 29 as small as possible, the lower end cap 17 is configured having a large volume and shaped such that it surrounds the outside of the diaphragm 31 facing it at a brief distance and its lower outside rests on the entire area of the bottom 3 of the housing 1. For delimiting the dead volume of the cavity 29 at the upper end, the holding part 33 is shaped such that it also surrounds the upper outside of the upper diaphragm 31 at a brief distance.

As already mentioned, with its compensating element formed by diaphragms 31, the compensating mechanism forms a type of hydropneumatic diaphragm accumulator in which the diaphragms 31 are secured at opposite ends of a retaining part 35, which is configured as a hollow body and which, along with the diaphragms 31, delimits the space 37 containing the compressible filling medium. In the exemplary embodiment shown, provision is made of a filler valve 39 for filling the space 37 using nitrogen gas. Obviously, provision can be made of a different kind of filling mechanism if use is made of a different kind of filling medium, for example a non-gaseous one, such as a foam material or the like. In a similar fashion and as is typical for diaphragm accumulators, the diaphragms 31 have a rim bulge 41 that is seated in a recess 43 formed on the given end edge of the retaining part 35. A supporting body 45 is provided for each diaphragm 31, which extends along the outside of the respective diaphragm 31 and which has fluid outlets. In the example shown, a cup-shaped perforated plate is provided as a supporting body 45, the end edge 46 of which engages over the facing end region 47 of the retaining part 33 and is fastened, for example welded, thereon. Instead of a perforated plate, a net or lattice structure could also be provided as a supporting body 45. For securing the compensating mechanism, the supporting body 45 of the diaphragm 31 (at the top in the figure) is bolted to the holding part 33 by means of a fastening screw 49 such that the entire compensating mechanism forms a component that can be removed through the opening 21 of the upper end cap 15, for example in order to fill the space 37 using process gas. The opening diameter of the opening 21 is slightly larger than the diameter of the holding part 33 and of the round retaining part 35, which has the same outer diameter. For an operation using aggressive fluids such as urea solutions, an elastomer that is compatible with these fluids such as ethylene propylene diene monomer rubber (EPDM) or hydrogenated acrylonitrile butadiene rubber (HNBR) can be provided as a material for the diaphragms 31. Ready-made diaphragms for diaphragm accumulators are available in these materials, hence existing identical components can be used in a cost-effective manner for the filter device according to the invention. 

1. A filter device for filtering fluid, particularly in the form of an aqueous urea solution, comprising a filter housing (1) and a filter element (11) arranged therein, as well as a compensating element (31) for compensating fluctuations in the pressure and/or volume of the fluid, characterized in that at least one elastically flexible diaphragm (31) serves as a compensating element, the diaphragm wall of which is held in a retaining part (35) and maintains a separation between the fluid and a compressible filling medium, such as a process gas.
 2. The filter device according to claim 1, characterized in that the diaphragm (31) is arranged on the downstream filtrate side (37) of the filter element (11).
 3. The filter device according to claim 1, characterized in that the diaphragm (31) is configured cup-like, spherical shell-like, or dome-like and is made of ethylene propylene diene monomer rubber (EPDM) or hydrogenated acrylonitrile butadiene rubber (HNBR).
 4. The filter device according to claim 1, characterized in that a bulge (41), which engages with an assignable recess (43) on the retaining part (35) in a form-fitting manner, is provided on the rim of the diaphragm (31).
 5. The filter device according to claim 1, characterized in that the cup-shaped diaphragm (31) is comparable to a diaphragm used in diaphragm-type hydraulic accumulators.
 6. The filter device according to claim 1, characterized in that an at least partially fluid-permeable supporting body (45) is arranged on the outside of the respective diaphragm (31), essentially following the outer contour thereof.
 7. The filter device according to claim 1, characterized in that the compensating element has two identically configured diaphragms (31), which are secured on opposite sides of the retaining part (35), which is configured as a hollow part and receives a process gas, preferably in the form of nitrogen gas, as a filling medium.
 8. The filter device according to claim 1, characterized in that the retaining part (35) has a filling mechanism (39) for the compressible filling medium.
 9. The filter device according to claim 1, characterized in that the compensating element (31) is surrounded at a predefinable radial distance by a cylindrical support tube (27) having fluid passages, the outer periphery of which cylindrical support tube supports the filter medium (13) of the filter element (11).
 10. The filter device according to claim 1, characterized in that the filter element (11) has two end caps (15, 17) between which the preferably pleated multi-layer filter medium (13) extends, wherein at least one (17) of said end caps at least partially fills in the filter housing (1), preferably at the bottom, in order to prevent dead volume and/or the other end cap (15) is penetrated by a preferably temperature-controllable holding block (33) for holding the compensating element (31) inside the filter housing (1).
 11. A filter element, in particular designed as an interchangeable element, preferably for a filter device according to claim 1, comprising at least two diaphragms (31) on opposite sides of a retaining part (35) that form components of the compensating element, and further comprising a filter medium (13) that envelops the compensating element and extends between two end caps (15, 17). 